This invention concerns the use of a mixture of nonionic and anionic surfactants to assist in the dewatering of aqueous slurries of cellulosic pulp.
Various surfactants have been used to assist in the removal of water from aqueous slurries or mats of fibrous materials. For Example, the use of anionic surfactants to assist in the dewatering of cellulosic papermaking slurries on a fourdrinier or cylinder machine is disclosed in International Patent Application Number PCT/US01/20276. A method of dewatering an aqueous mineral wool slurry on fourdrinier machine assisted by an anionic, nonionic or cationic surfactant is disclosed in U.S. Pat. No. 4,062,721. There exists, however, an ongoing need for improved additives to improve the efficiency and flexibility of the dewatering process, particularly for market pulps, which are prepared at one site and then transported to the papermaking site.
We have discovered that using a combination of nonionic and anionic surfactants in a process for dewatering aqueous cellulosic slurries results in increased dewatering effectiveness over the use of either surfactant alone.
Accordingly, in its principal aspect, this invention is directed to a method of dewatering an aqueous cellulosic pulp slurry comprising
a) adding to an aqueous slurry of washed cellulosic pulp an effective dewatering amount of a mixture of one or more nonionic surfactants and one or more anionic surfactants; and
b) dewatering the pulp.
Use of nonionic surfactants in combination with anionic surfactants makes the anionic surfactants more efficient as a dewatering aid, allowing the same effectiveness (in terms of consistency improvement) at lower anionic surfactant dose and further provides the ability to achieve effectiveness levels not possible using anionic surfactants alone.
Lowering the anionic surfactant dose also decreases the amount of cationic demand introduced to the mill""s water systems.
Finally, the dual surfactant system of this invention allows for greater flexibility in tailoring a dewatering program to a particular machine""s dewatering needs regarding performance, runnability, and cost.
Definitions of Terms
xe2x80x9cAlcohol Alkoxy Sulfatexe2x80x9d means an anionic surfactant compound of formula R2O(R3CH2CH2O)xSO3xe2x88x92M+ where R2 is C8-C18 alkyl, R3 is absent or methylene a from 1 to about 50. The alcohol alkoxy sulfate may be in the salt form where M a counterion such as Na, K, Mg, NH4, and the like, or in the acid form where M is H. Representative alcohol alkoxy sulfates include sodium and ammonium lauryl ether sulfate. Alcohol alkoxy sulfates are available from Stepan Company, Northfield, Ill.
xe2x80x9cAlcohol Alkoxylatexe2x80x9d means a nonionic surfactant compound of formula R6O(C2H4O)x(C3H6O)yH where R6 is C8-C24 alkyl, x is 1-20 and y is 1-20. the alcohol alkoxylate is prepared by reacting a C8-C24 alkyl alcohol, or mixture of C8-C24 alkyl alcohols, both designated herein as R6OH, with propylene oxide and optionally ethylene oxide. The ethylene oxide and propylene oxide may be added in random or block fashion. Alcohol alkoxylates are available from Huntsman Corporation, Houston, Tex.
xe2x80x9cAlcohol Ethoxylatexe2x80x9d means a nonionic surfactant compound or mixture of compounds of formula R1O(CH2CH2O)nH where R1 is C5-C25 alkyl or C5-C25 hydroxyalkyl and n is 1-30. Preferred alcohol ethoxylates are those where R1 is C8-C18 alkyl or C8-C18 hydroxyalkyl and n is 1-20. Alcohol ethoxylates are available from Union Carbide, Danbury, Conn. under the tradename Tergitol and from Sasol North America Inc., Houston, Tex. under the trade name Alfonic.
xe2x80x9cAlcohol Sulfatexe2x80x9d means compounds of the formula R2OSO3M, where R2 and M are defined herein. Representative alcohol sulfates include sodium dodecyl sulfate, tetradecyl sulfate, ammonium lauryl sulfate, magnesium lauryl sulfate, cetyl sulfate, octyl sulfate, nonyl sulfate, decyl sulfate, 4-undeconal, 7-ethyl-2-methyl-sulfate, sodium salt (Niaproof Anionic Surfactant 4, available from Niacet Corporation, Niagra Falls, N.Y.), and the like.
xe2x80x9cAlkoxyxe2x80x9d and xe2x80x9calkoxylxe2x80x9d mean an alkyl-Oxe2x80x94 group wherein alkyl is defined herein. Representative alkoxy groups include methoxyl, ethoxyl, propoxyl, butoxyl, and the like.
xe2x80x9cAlkylxe2x80x9d means a monovalent group derived from a straight or branched chain saturated hydrocarbon by the removal of a single hydrogen atom. Representative alkyl groups include methyl, ethyl, n- and iso-propyl, and the like.
xe2x80x9cAlkyl phenol ethoxylatexe2x80x9d means a nonionic surfactant compound of formula R5O(CH2CH2O)pH where R5 is phenyl, optionally substituted with one or two C8-C12 alkyl groups and p is 1-30 Preferred alkyl phenol ethoxylates are those where where R5 is phenyl substituted with C9 alkyl and p is 1-20 Alkyl phenol ethoxylates are available from Rhodia Inc., Cranbury, N.J. under the trade name Igepal.
xe2x80x9cAlkylenexe2x80x9d means a divalent group derived from a straight or branched chain saturated hydrocarbon by the removal of two hydrogen atoms. Representative alkylene groups include methylene, ethylene, propylene, and the like.
xe2x80x9cArylxe2x80x9d means an aromatic monocyclic or multicyclic ring system of about 6 to about 20 carbon atoms, preferably of about 6 to about 10 carbon atoms. Aryl also includes ring systems where two aryl groups are connected through alkylene, alkenylene or alkynylene groups. The aryl is optionally substituted with one or more alkyl, alkoxy or haloalkyl groups. Representative aryl groups include phenyl, biphenyl, naphthyl, cis- and trans-stilbene, biphenylmethyl, diphenylacetylene, and the like.
xe2x80x9cArylalkylxe2x80x9d means means an aryl group attached to the parent molecular moiety through a C1-C8 alkylene group. C1-C2 alkylene groups are preferred. Representative arylalkyl groups include phenylmethyl, phenylethyl, phenylpropyl, 1-naphthylmethyl, and the like.
xe2x80x9cCellulosic pulpxe2x80x9d means a mixture of fibers derived from kraft or sulfite pulping of cellulosic materials such as wood. Representative cellulosic pulps include bleached and unbleached pulps and dissolving pulps. Typical bleached pulps contain about 60 to about 70 percent cellulose, about 30 to about 40 percent hemicellulose and less than about one percent lignin. Unbleached pulps generally contain about 65 to about 75 percent cellulose, about 20 to about 30 percent hemicellulose and up to about 5 percent lignin. Dissolving pulps are about 100 percent cellulose.
xe2x80x9cCycloalkylxe2x80x9d means a non-aromatic mono- or multicyclic ring system of about 5 to about 10 carbon atoms. Preferred ring sizes of rings of the ring system include about 5 to about 6 ring atoms. The cycloalkyl is optionally substituted with one or more substituents selected from alkyl, alkoxy and haloalkyl. Representative cycloalkyl include cyclopentyl, cyclohexyl, cycloheptyl, and the like.
xe2x80x9cDialkyl sulfosuccinatexe2x80x9d means an anionic surfactant compound of formula R9OOCCH2CH(SO3M)COOR10, where R9 and R10 are independently selected from amyl, octyl, 2-ethyl hexyl, isobutyl, tridecyl, or lauryl and M is as defined herein. A representative dialkyl is dioctylsulfosuccinate. Dialkyl sulfosuccinates are commercially available from Cytec Industries, West Patterson, N.J.
xe2x80x9cFatty Acid Ethoxylatexe2x80x9d means a nonionic surfactant compound of formula R7COO(CH2CH2O)rH where R7 is C7-C25 alkyl and r is 1-30. Fatty acid ethoxylates are commercially available from Henkel Corporation, Emery Group, Ambler, Pa.
xe2x80x9cHydroxyalkylxe2x80x9d means a C1-C8 alkyl substituted by one to three hydroxyl groups with the proviso that no more than one hydroxy group may be attached to a single carbon atom of the alkyl group. Representative hydroxyalkyl include hydroxyethyl, 2-hydroxypropyl, and the like.
xe2x80x9cMarket pulpxe2x80x9d means chemical paper grade pulps which are typically sold on the open market to non-integrated paper mills (i.e. paper mills not having a pulp mill on-site). Market pulp also includes fluff pulp, which is used in diapers and related sanitary products, and dissolving pulp which is used in rayon manufacture. End uses for market pulp include paper and board manufacture, absorbent products (diapers, feminine care products, etc.), nonwovens, rayon and other cellulose derivatives.
xe2x80x9cPulp Slurryxe2x80x9d means a slurry of cellulosic pulp as defined herein in water. Typical pulp slurries have a consistency (weight percent of cellulosic fibers) of about 0.2 to about 4 percent. Typical market pulp slurries have a consistency of about 0.5 to about 2 percent.
xe2x80x9cSulfonatexe2x80x9d means an anionic surfactant compound of the formula R8SO3M where R8 is C8C18 alkyl, a C3-C12 cycloalkyl, C8-C18 aryl or C8-C18 alkylaryl group. Representative sulfonates include dodecyl sulfonate, tetradecyl sulfonate, alkylbenzenesulfonic acids (ABSA) and salts of alkylbenzenesulfonic acids, alkylbenzenesulfonates (ABS), linear alkylbenzenesulfonates, paraffin sulfonates, petroleum sulfonates and alpha olefin sulfonates. Sulfonates are available commercially from Stepan Company, Northfield, Ill.
xe2x80x9cSulfosuccinic acid ester with ethoxylated alcoholsxe2x80x9d means an anionic surfactant compound of formula R11(OCH2CH2)tOOCH(SO3M)CH2COOM where R11 is C8-C18 hydroxyalkyl, t is an integer from 1 to about 10 and M is as defined herein. A representative sulfosuccinic acid ester with ethoxylated Alcohol is laureth sulfosuccinate (Schercopol LPS, available from Scher Chemicals, Inc., Clifton, N.J.).
This invention is a dual surfactant system comprising one or more anionic surfactants and one or more nonionic surfactants for improving the dewatering of an aqueous cellulosic pulp slurry.
In a preferred aspect of this invention, the anionic surfactants are selected from the group consisting of alcohol sulfates, alcohol alkoxy sulfates, sulfonates, dialkyl sulfosuccinates and sulfosuccinic acid esters with ethoxylated alcohols.
In another preferred aspect, the nonionic surfactants are selected from the group consisting of alcohol ethoxylates, alkyl phenol ethoxylates, fatty acid ethoxylates and alcohol ethoxylates.
In another preferred aspect, the anionic surfactant is selected from the group consisting of alcohol sulfates and alcohol alkoxy sulfates and the nonionic surfactant is selected from the group consisting of alcohol ethoxylates and alkyl phenol ethoxylates.
In another preferred aspect, the anionic surfactants are selected from the group consisting of sodium dodecylsulfate and sodium lauryl ether sulfate.
In another preferred aspect, the nonionic surfactants are selected from the group consisting of secondary linear alcohol ethoxylates and nonylphenol ethoxylates.
The optimal amounts of anionic and nonionic surfactant are empirically determined based upon the characteristics of the pulp being dewatered. In general, the dose of anionic surfactant is from about 0.05 to about 10 lb/ton, preferably from about 0.25 to about 0.75 lb/ton, based on pounds of active ingredient per ton of dry pulp. The dose of nonionic surfactant is typically from about 0.001 to about 10 lb/ton, preferably from about 0.25 to about 0.75 lb/ton, based on pounds of active ingredient per ton of dry pulp.
The anionic and nonionic surfactant can be added in any order or simultaneously.
The surfactants are mixed with the pulp after it has been washed (to remove residual pulping/bleaching chemicals), and before the pulp is vacuum dewatered during the mat consolidation process. For example, the surfactants may be added just prior to the headbox on a fourdrinier pulp dryer.
In another preferred aspect of this invention, an effective amount of one or more defoamers is added to the pulp slurry.
Representative defoamers include C8-C48 alcohols in water with an emulsifier, C8 to C48 alkoxylated alcohols, such as ethoxylated propoxylated alcohols, silicones, wax (in ppm levels only), silica and ethylene bis stearamide (particulate suspended in oil) compounds, and blend(s) of a triglyceride ester and a polyethylene glycol ester. A preferred defoamer is a 10% actives blend of C16 and C18 alcohols. Defoamers are available from Ondeo Nalco Company, Naperville, Ill. or other companies, or can be readily synthesized using techniques known in the art.
The optimal amount of defoamer is empirically determined based upon the characteristics of the pulp being dewatered. In general, from about 0.5 to about 10 lb/ton, preferably from about 1 to about 3 lb/ton, based on pounds of defoamer product per dry ton of pulp is used.
The defoamer may be added before, after or simultaneously with the anionic and nonionic surfactants.
In another preferred aspect of this invention, an effective amount of one or more coagulants is added to the pulp slurry.
Representative coagulants include polyamines including dimethylamine-epichlorohydrin, polyamidoamines including condensation polymers of diethylene triamine and adipic acid, polyethyleneimine, poly(diallyldimethylammonium chloride), EDC/NH3 polymers, acrylamide/dimethylaminoethyl methacrylate methyl chloride salt copolymer, acrylamide/dimethylaminoethylacrylate methyl chloride salt copolymer, poly(dimethylaminoethylacrylate methyl chloride salt), poly(dimethylaminoethyl methacrylate methyl chloride salt), polyacrylic acid and salt thereof, acrylic acid/diallyldimethylammonium chloride copolymer, acrylamide/diallyldimethylammonium chloride copolymers, alum, polyaluminum chloride and other aluminum based coagulants, polyvinylamine, and copolymers of vinylamine with vinylformamide, vinyl acetate, vinyl alcohol, and acrylamide.
All of these coagulants are available commercially or can be readily synthesized using techniques known in the art.
Typical coagulant dose is from about 0.1 to about 20 lb/ton, preferably from about 0.2 to about 10 lb/ton and more preferably from about 0.5 to about 6 lb/ton, based on polymer actives per dry ton of pulp.
The coagulant is added before, after or simultaneously with the addition of the anionic and nonionic surfactants. Preferably, the coagulant is added before the surfactants and before the defoamer, if a defoamer is added.
After addition of the nonionic and anionic surfactants, coagulants and defoamers, the pulp is dewatered, preferably on a xe2x80x9cfourdrinierxe2x80x9d or xe2x80x9ccylinderxe2x80x9d machine.
In a fourdrinier machine, the pulp (also known as a xe2x80x9cstock slurryxe2x80x9d at from about 0.5 to about 2 percent consistency) is deposited from a headbox onto a continuous, moving open mesh fabric. The water in the slurry drains through the fabric thus forming a pulp mat. After the initial free drainage through the fabric or wire, the mat is further dewatered as it is carried on the wire by the application of progressively increasing vacuum. The vacuum is applied to the underside of the mat by a series of elements known as vacuum boxes. Vacuum may also be applied at the couch roll, just prior to the removal of the mat from the forming fabric. Nominal mat consistency at this point is about 16% to about 20%. The pulp mat then enters the press section of the machine, which typically consists of from two to four press nips, where further water is removed by mechanical expression. The nominal mat consistency after pressing is from about 40% to about 45%. After the press section, further water is removed by evaporative means, typically by hot air impingement. The final consistency of the sheet is typically in the range of from about 81% to about 86% (oven-dry basis) or from about 90% to about 95% (air-dry basis).
In a cylinder machine, the stock slurry is contained in a vat and a rotating, fabric-covered cylinder is used in forming the mat. The stock in the vat is picked up onto the cylinder and drainage of water occurs through the fabric/screen to form the mat. The mat is further vacuum dewatered on the cylinder, whereupon it is transferred to a press section and dryer section as described for the fourdrinier machine.
Dewatering can be maximized by working to achieve optimal performance of the mechanical water removal sections (vacuum, press, and dryer). In order to maximize dewatering, the stock temperature is kept as high as possible, typically as high as from about 150 xc2x0 F. to about 160 xc2x0 F. (about 65xc2x0 C. to about 71xc2x0 C.) to enhance water removal by lowering the water viscosity. Also, steam boxes can be used to increase the temperature of the mat prior to the press section. The pulp pH is kept low, from about 4 to about 5, so that the fibers are less swollen and drain more easily.
The foregoing may be better understood by reference to the following Examples, which are presented for purposes of illustration and are not intended to limit the scope of this invention.
In the following Examples, xe2x80x9cSDSxe2x80x9d means sodium dodecyl sulfonate; xe2x80x9cNPExe2x80x9d means nonylphenol ethoxylate; xe2x80x9cLAE 1xe2x80x9d means a C11-C15 secondary linear alcohol ethoxylate containing 5 moles of ethoxylation (Tergitol 15S-5, Union Carbide, Danbury, Conn.); xe2x80x9cLAE 2xe2x80x9d means a C11-C15 secondary linear alcohol ethoxylate containing 7 moles of ethoxylation (Tergitol 15S-7, Union Carbide, Danbury, Conn.); xe2x80x9cLAE 3xe2x80x9d means a C11-C15 secondary linear alcohol ethoxylate containing 9 moles of ethoxylation (Tergitol 15S-5, Union Carbide, Danbury, Conn.); xe2x80x9cNPE 1xe2x80x9d means a nonylphenol ethoxylate containing 5 moles of ethoxylation (Igepal CO-520, Rhodia Inc., Cranbury, N.J.); xe2x80x9cNPE 2xe2x80x9d means a nonylphenol ethoxylate containing 8.5 moles of ethoxylation (Igepal CO-620, Rhodia Inc., Cranbury, N.J.); xe2x80x9cNPE 3xe2x80x9d means a nonylphenol ethoxylate containing 12 moles of ethoxylation (Igepal CO-720, Rhodia Inc., Cranbury, N.J.).
Drainage performance is evaluated by measuring vacuum break time using a VDT instrument. During VDT testing, the furnish is drained through an Ahlstrom 1278 filter paper (available from Ahlstrom Filtration, Inc, Mount Holy Springs, Pa.) under applied vacuum to form a pad. The time required to drain 400 ml of filtrate and the time required for removal of a continuous water phase from the pad (vacuum break time) are recorded. The vacuum pump is operated for one minute after the vacuum break and the vacuum value, referred to as the final pad vacuum, is recorded. The pad is removed from the VDT+ instrument, weighed, and dried in an oven at 105xc2x0 C. The weight of the dry pad is used to determine the pad consistency.
The vacuum break time is a measure of the rate of water removal from the pulp. The final pad vacuum is inversely proportional to the air permeability of the pad. Good formation gives greater resistance to air channeling, resulting in a higher final pad vacuum. The pad consistency is a measure of the total extent of water removal. Higher pad consistencies correlate to increased dewatering efficiency.